This invention relates to means for combining images sensed through lenses of different focal lengths, and particularly to lenses for improving human vision.
A common defect in human vision is the inability of the eye to focus an image on the retina. The myopic eye fails to focus distant objects on the retina whereas the presbyopic eye fails to focus nearby objects on the retina. Myopia and presbyopia can each be corrected by appropriate but different lenses. The lenses of conventional bifocal eyeglasses consist of an upper lens segment for correct distance vision and a lower lens segment for correct near vision. The upper and lower lens segments are joined along a horizontal line.
When the user of conventional bifocal lenses views a distant object, the light that passes through the upper segments of the right and left lenses is focused on the lower portion of the corresponding retina but the light that passes through the lower segments of the lenses falls on the upper portion of the corresponding retina where it is not in focus. Thus the partial retinal image formed by the light that passes through the lower lens segments is blurred.
Similarly, when the user of conventional bifocal lenses views a nearby object, the partial retinal image formed by the light that passes through a lower lens segment is correctly focused on the upper portion of the retina and is therefore sharp but the partial retinal image formed by the light that passes through the upper lens segment is not in focus on the lower portion of the retina and that image is consequently blurred. Thus, conventional bifocal lenses produce retinal images that are partly in focus and partly blurred in corresponding parts of both retinas. This property of conventional lenses can cause difficulties for the use in certain viewing circumstances.
For example, when descending a staircase, the gaze is normally directed downward. Thus the line of sight from the stairs to the retina will pass through the lower lens segment and form a blurred partial retinal image on the upper parts of both retinas. The use of a desktop personal computer provides another example. In this case the computer keyboard is typically located in such a position that the line of sight from the keys to the retina will pass through the lower lens segments. Since the keyboard is near the eyes, this partial retinal image will be in focus. But the display screen is typically located at eye level and the line of sight from the display screen to the retina will pass through the upper lens segments. Since the information displayed on the screen typically consists of text and other material that incorporates fine detail which must be near the eyes in order to be seen, this partial retinal image will be blurred on corresponding parts of both retinas.
Various type of bifocal and multifocal lenses have been used in the past to solve particular problems. For example, in Kozol, Optical Journal Review, Apr. 1, 1963, "The History, Theory and Application of Multifocal Lenses - XIII", pages 27--31, and Obrig, Modern Ophthalmic Lenses and Optical Glass, Obrig Laboratories Incorporated, New York, New York 1944, pages 266-267, several different arrangements of lenses are discussed. These include trifocal lenses, which have intermediate focusing lens segments as well as near focusing and distant focusing lens segments, and lens arrangements which allow the user to focus at one distance when looking to the right and another distance when looking to the left.
More specifically, the Optical Journal Review article discloses at pages 29 and 30 vertical segment vocational bifocals in which, as shown in FIG. 34 L on page 30, lenses are proposed having a distance correction to the right of the nasal pupillary border of the user's left eye and to the right of the temporal pupillary border of the right eye. Segments having an intermediate distance correction are located to the left of the respective nasal and temporal pupillary borders. Also, as shown in FIG. 34 M at page 30 of the Optical Journal Review article, the distance correction may be to the left and the intermediate correction to the right of the pupillary borders.
FIGS. 1 A and 1 B shows prior art bifocals of this type viewed from the side of the lenses facing the wearer wherein the numeral 10 designates a frame for supporting left and right lenses 12 and 14, 16 l and 16 r lens segments of the left and right lenses 12 and 14 which are respectively ground to correct for objects located at a relatively great distance from the user and 18 l and 18 r lens segments of the left and right lenses which correct for objects closer to the viewer. In FIG. 1 A, the lens segments 16 l and 18 l are joined along a vertical line 20 situated at the nasal pupillary border (i.e., at that edge of the pupil nearest to the wearer's nose) and lens segments 16 r and 18 r along a vertical line 22 situated at the temporal pupillary border of the user (i.e., at that edge of the pupil nearest to the wearer's temple). The location of the wearer's pupils, designated by circle 24 l and 24 r, would be to the left of the pupillary borders and therefore the lenses 18 l and 18 r, ground to correct for images located at an intermediate distance from the use, would be in front of the pupils when the user is looking straight ahead. Conversely, in FIG. 1 B, the lens segments 16 l and 18 l are to the left and right respectively of a vertical line 22' situated at the temporal pupillary border and the lens segments 16 r and 18 r to the left and right respectively of a vertical line 20' located at the nasal pupillary border.
Prior art lenses of this type may be used by artists or musicians who must focus on a canvas or music stand positioned at an intermediate distance to their one side and a model or conductor located further away on their other side. The bifocals of FIG. 1 A would therefore be used by an artist or musician whose canvas and music are at an intermediate distance to his left and the model or conductor at a greater distance to his right. The bifocals of FIG. 1 B would be used when the scenes being viewed were reversed.
These known lens arrangements having vertically oriented lens segments have the same disadvantage as conventional bifocal lenses. That is, under commonly occurring conditions in which both near and far objects occupy both right and left halves of the field of vision, the retinal images that are produced are partly in focus and partly blurred in corresponding parts of both retinas. Thus, these prior art bifocals, which are designed for a specific type of viewing situation, are no better than conventional bifocals if the specific viewing situation for which they are designed is not present.
The purpose of the present invention is to eliminate these and similar problems of conventional bifocal lenses.